Another heater question

[jase386]

85 Caprice New Radiator and 195 Thermostat all installed yesterday. Heat still blows cool when car stopped.

will a bad heater control valve show the same symptoms or could it be with the in dash thermostat and vaccum system?


thanks for any input

[Blue Bowtie]

If the temperature is normal or adequate while the engine is running at speed, but is inadequate at idle, there may be a coolant flow problem or air bubble in the system. Since the thermostat was just replaced, monitor the coolant level for several days to be sure the system remains full. Entrapped air and dissolved air in the water will liberate after heat/cool cycles (Yes, air dissolves in water, which is why boilers have deaerating systems).

Once the coolant level is verified, feel the hoses while the engine is running. If the heater hoses are not hot, there may be a restriction in the core, a problem with a hot water valve (although I don't think B-cars had those until about 1987-88), or inadequate output flow from the pump. The likelihood of a core restriction or hot water valve problem is low if the heat produced is adequate when the engine is running at higher RPM. That would point to a worn pump impeller or incorrectly assembled pump (reverse-rotation/serpentine impeller or pump installed in a standard V-belt installation).

AFAIK, the hot water valve default position is open, and they require vacuum to close. I might be mistaken about that on your vehicle, but that's how others operate.

[silicon212]

Originally Posted by Blue Bowtie

a problem with a hot water valve (although I don't think B-cars had those until about 1987-88)

That's actually my feeling about the issue - btw the B cars had these valves starting in the mid-70s. My old '82 had one back in the day.

Another way to see the effect of air in hot water is to draw a glass of hot water from the tap - notice it has that milky appearance. That's the air in the water and if you hold your ear to it, you can hear it 'fizz'.

[Blue Bowtie]

I know some '70s vehicles used them, and some didn't. Then some of them went away, and some of them came back. My '67 Firebird and '71 Olds didn't have them, but '78 Caddy did. I cannot recall if my '85 Caprice Estate Wagon had one, but by your information, it probably did. Their use seems to have no rhyme nor reason. The B-Cars got rid of them for good by 1994, but I'm not sure whether any remained in other applications after that.

[jase386]

so youre saying to just wait and the bubble will fix itself if there is one? if not, how do you get the bubble from the system?

the heat problem was happening before we replaced the radiator and thermostat.

[Blue Bowtie]

Since the condition existed before the system was drained and refilled, I'd suspect one of the other possibilities. Does the core get heat with the engine RPM increased?

[bobss396]

My '84 has the vacuum line going to the valve. If the valve is original you should be able to actuate it one way of the other to simulate a heat or no-heat condition. Chances are that the diaphragm inside is shot.

I doubt that the heater core would be totally blocked all of a sudden unless someone recently added something like Barrs Stop Leak. You should get some heat with a blocked core, a bad heater control valve can give you a no heat condition.

Bob

[willz0072002]

hey...i have the EXACT same problem..heater blows hot only on freeway..cools down when stopped...temperature guage reads accuratly...wtf?? ill keep watching this post as it is 24 degrees here in WA right now!!